Question 37F1

NAVTEX (NAVigational TEXt) stations on 518 kHz avoid mutual interference through a combination of techniques. Primarily, transmissions are **scheduled on a time-sharing basis** using Time Division Multiple Access (TDMA). Each station is allocated a specific 10-minute time slot within a four-hour cycle, preventing simultaneous transmissions from multiple stations that might be received by a single vessel. Additionally, **transmitter power is limited**, which restricts the service area of each station, reducing the likelihood of a receiver picking up signals from distant, out-of-area stations transmitting in different time slots. Finally, **station assignment codes** (the B1 character in a NAVTEX message) are unique within a geographical area (NAVAREA) and allow receivers to be programmed to accept messages only from specific, relevant stations, effectively filtering out transmissions from other, potentially interfering stations. Options B and C are incorrect because NAVTEX stations do *not* transmit at the same time and are not limited to daytime operation only. Option D is incomplete and less accurate than A, missing the crucial detail of power limitations in the context of avoiding local mutual interference.